1. Field of the Invention
The present invention relates to an input device using strain gages, which is suitable for use in a computer or the like.
2. Description of the Related Art
In a conventional input device using strain gages, as shown in FIG. 21, a control member 51, which is made of a flexible synthetic resin of polyphenylene ether, comprises a prismatic control portion 51a, three platelike base portions 51b, 51c, and 51d radially extending from the bottom of the control portion 51a at right angles to one another, and a linking portion 51e for linking the three base portions 51b, 51c, and 51d at the bottom of the control portion 51a. This control member 51 is mounted by an appropriate means on a frame 50 of a keyboard used in a computer.
When the control portion 51a of the control member 51 is tilted down in the X1-, X2-, Y1-, and Y2-directions, the base portions 51b, 51c, and 51d are correspondingly bent. The amount of bending changes according to the amount of tilting of the control portion 51a. 
Such a control member 51 is produced by molding. A mold is prepared which includes a space portion that conforms to the shape of the control member 51, and an inlet C that is formed at a position corresponding to the end of the base portion 51c (see FIG. 21), and a liquid synthetic resin is injected from the inlet C into the space portion.
A flexible substrate 52 made of polyester has, on one side thereof, two strain gages 53 and 54 formed of resistors, and lead wires 55 and 56 printed in a conductive ink of sliver so as to be connected to the strain gages 53 and 54.
The opposite side of the flexible substrate 52 from the side where the strain gages 53 and 54 are formed is partly and directly bonded by an adhesive onto the upper surfaces of the base portions 51b and 51c that are arranged at right angles, so that one of the strain gages 53 is positioned on the base portion 51b, and the other strain gage 54 is positioned on the base portion 51c. 
During operation of such an input device, when the control portion 51a of the control member 51 is tilted down in the X1-direction, the upper side of the base portion 51b is bent to stretch, and the strain gage 53 thereon is also stretched, thereby increasing the resistance. When the control portion 51a is tilted down in the X2-direction, the upper side of the base portion 51b is bent to be compressed, and the strain gage 53 thereon is also compressed, thereby decreasing the resistance.
In contrast, when the control portion 51a is tilted down in the Y1-direction, the resistance of the strain gage 54 increases on the same principle as above. When the control portion 51a is tilted down in the Y2-direction, the resistance of the strain gage 54 decreases.
FIG. 22 is a circuit diagram of a voltage detecting circuit in the conventional input device. The strain gages 53 and 54 are connected at one end, and are further connected to the ground G. The other ends of the strain gages 53 and 54 are connected to a terminal Tx and a terminal Ty, respectively, from which the voltage divided by a resistive potential divider in the circuit is output. The above-described change in resistance is detected as a change in voltage, and the computer reads the voltage change and controls a cursor so that the cursor moves vertically or horizontally in response to the movement of the control portion 51a in the X1- and X2-directions, or in the Y1- and Y2-directions.
As described above, the control member 51 of the conventional input device is produced by molding in which a liquid synthetic resin is injected from the inlet C of the mold at a position corresponding to the end of the base portion 51c. Therefore, the liquid synthetic resin does not flow smoothly during molding. In particular, it is impossible to give the same thickness to the base portions 51b, 51c, and 51d, which lowers accuracy.
Furthermore, since the control member 51 is made of a synthetic resin of polyphenylene ether, the creep property of the base portion 51b is undesirable, and accurate bending is impossible. In addition, the control member 51 has a low heat resistance, and therefore, is not suitable for use in high-temperature environments.
Accordingly, it is an object of the present invention to provide an input device in which a plurality of strain gages have identical characteristics, in particular, when glass fiber is used.
In order to achieve the above object, according to an aspect of the present invention, there is provided an input device including a control member having a control portion, a plurality of beam portions connected at one end to the control portion so as to extend perpendicularly to the axis of the control portion, and a flat base portion connected to the other end of the beam portions; and a strain gage disposed on the beam portions, wherein the control member is formed by molding with the top end of the control portion used as an inlet.
Preferably, the control member is made of a synthetic resin containing glass fiber.
According to another aspect of the present invention, there is provided an input device including a control member having a control portion, and a plurality of base portions connected at one end to the control portion so as to extend perpendicularly to the axis of the control portion; and a strain gage disposed on the base portions, wherein the control member is formed by molding with the top end of the control portion used as an inlet.
Preferably, the control member is made of a synthetic resin containing glass fiber.
Further objects, features, and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.